1. Field of the Invention
This invention relates to mortar compounds for setting tile and, in particular, for setting ceramic tile. The invention relates specifically to dry-set mortar compositions which are sag-resistant.
2. Description of the Prior Art
At present tile and, particularly ceramic tile, is set in many cases by dry-set Portland cement mortars. For many years the Portland cement compositions used required a very thick bed and generally also required a mortar coat for setting the tile. Eventually, these thick-mud-method Portland cement mortars were replaced to a great extent by thin-bed Portland cement dry-set mortars. Typical dry-set mortars are thin-bed mortars and are principally comprised of Portland cement, sand, a water retentive cellulose ether, such as methyl cellulose or hydroxyethyl cellulose. Water is added prior to use. U.S. Pat. No. 2,934,932 (Wagner; issued May 3, 1960) and U.S. Pat. No. 3,243,932 (Selden; issued Mar. 29, 1966) are illustrative of the dry-set mortars which are currently used to set tile in thin beds. On other occasions a rubber or polymer latex is added to the dry mix to make a mortar, which is then called a latex Portland cement mortar. The latex may contain some of the additives in solution that otherwise would be part of the dry mix.
One of the many properties required by mortar for setting tile is that it be sag resistant. Sag resistance is a term used in the trade and defined by a test method that is part of the American National Standard Specification for Dry-set Portland Mortar Cement -- A 118.1. Sag-resistance is a property or a characteristic relating to the ability of the mortar to resist movement under load until a certain load level is reached. This property or characteristic is vitally important in dry-set mortars and also to a latex mortar since a mortar to be practically functional, must be in a slurry or paste form on the one hand, but also must be capable of supporting the load imposed on it by the tiles being set. It is vital that the mortar support the tile without any appreciable sinking of the tile into the mortar during the period in which the mortar sets. In wall applications sag resistance is even more critical because the mortar must hold the tile in position on the wall during the period in which the mortar is setting.
At present, short asbestos fibers are used to provide dry-set mortars with sag-resistant characteristics. Illustrative of the dry-set mortar compositions having fibers to resist sag are U.S. Pat. No. 3,030,258 (Wagner; issued Apr. 17, 1962) and U.S. Pat. No. 3,243,307 ( Selden; issued Mar. 29, 1966). Although the asbestos fibers and fibers in general are suitable for providing dry-set mortars with sag-resistant properties, asbestos fibers and fibers in general have been found to be dangerous to the health of persons who ingest them into their lungs and the use thereof has recently been limited by national safety laws.